1. Field of the Invention
The present invention relates to a process for treating a zein containing raw material followed by a zein extraction process, and more particularly, for treating the material to decrease smell and color tone thereof.
2. Related art
Zein is a main ingredient of corn proteins and dissolves in various alcohols and alkali solutions. Zein has adhesiveness and a property to form films and fibers. When a zein solution is coated by spraying, dipping or the like on an outer surface of an object and dried, a film is formed thereon. The film has excellent resistance to water, acid and heat as well as in electric insulation property. Therefore, zein has widely been employed as a raw material for preparing waterproof stuff for papers, paint for wood works, adhesive for plywood, damp-proofing agents, coating agent for foods and tablets (medicine), and the like.
Various processes have been proposed for extracting and purifying the zein.
In Jap. Pat. No. Sho 61 (year of 1986 ) - 167700 (A) and Martinue NiJhoff et al "Seed Proteins Biochemistry, Genetics, Nutritive Value", page 275-285 (1983) , there are described extraction processes , wherein corn gluten meal or the like material containing the zein is extracted with 70-90% (V/V) ethyl alcohol , about 90% (V/V) isopropyl alcohol or a similar water-containing lower alcohol, then the alcohol is distilled out to obtain the zein. In Jap. Pat. No. Sho 50 (year off 1975 )-16800(B) , there is described a process, wherein the zein is extracted from wheat gluten with 60-95% (V/V) aqueous acetone, methylethylketone or diethylencglycol solution and stirring at temperature of 50-70.degree. C., which is an application of Carter et al., related art to U.S. Pat. No. 3,535,305.
The zein obtained by the above conventional processes has an inherent color and smell and thus can not sufficiently satisfy recent severe requirements for lack of odor and color in food and medicine preparation industries. Besides, it is difficult to stably supply the zein product with consistent quality, because of a fluctuation in the quality of raw materials, when such a conventional process is applied for.
As processes for purifying zein, there are those wherein the zein containing alcohol or alkali solution is cooled to cause a precipitation of the zein and the resulting block-like precipitate is dried ["Industrial and Engineering Chemistry", Vol . 33, No . 3 , page 394 (1941) ], and wherein the zein solution is poured into water or a salt solution, for instance sodium chloride solution, to cause a precipitation of the zein, and the resulting precipitate is dried to obtain the zein product which has good solubility in ethyl alcohol [Jap. Pat. No. Sho 63 (year of 1988)-185999(A) ].
The former process has disadvantages in that the block-like precipitate is difficult to wash and the solution should be kept at the temperature of -20.degree. C. or below to avoid denaturation of the zein due to water contained therein. The severe cooling condition and subsequent drying increase cost. The latter purification process has also disadvantages in that the color and smell can not sufficiently be removed , cooling reservation of the precipitate is required to avoid denaturation and freeze-drying of the precipitate requires an increase in cost.